A chemical absorption method is known as a method for removing and recovering CO2 from combustion exhaust gas from thermal power stations and steel works. A known apparatus for recovering CO2 using a chemical absorption method generally has an absorption tower and a regeneration tower. In the absorption tower, CO2 is absorbed into an amine compound aqueous solution (hereinafter referred to as an amine solution) at 40° C. to 50° C. The amine solution with CO2 absorbed therein (hereinafter referred to as a rich solution) is supplied to the regeneration tower. The regeneration tower is modeled after a general distillation tower, and is structured such that a rich solution supplied dropwise into the regeneration tower comes in countercurrent contact with ascending vapor, thus heating the rich solution. As a result, CO2 is desorbed from the rich solution (since the gas obtained by the desorption includes saturated vapor, the gas is hereinafter referred to as vapor-containing CO2). The amine solution resulting from the CO2 desorption from the rich solution is heated by externally introduced high-temperature steam in the regeneration tower or in a reboiler connected to the regeneration tower, thereby generating vapor from the amine solution. The generated vapor is introduced from a lower portion of the regeneration tower and heats the rich solution, as mentioned above. The vapor-containing CO2 generated in the regeneration tower is cooled as it comes out through the top of the regeneration tower, thereby removing the moisture from the vapor-containing CO2 to recover CO2. The amine solution from which the CO2 has been desorbed (hereinafter referred to as a lean solution) is cooled to 40° C. to 50° C., and is supplied to the absorption tower to be reused.
The CO2 recovery by the above known apparatus is performed by heating an amine solution in a regeneration tower or in a reboiler connected to the regeneration tower using high-temperature steam of about 120° C., thereby generating vapor from the amine solution. As a result, the amine solution can be heated to a high temperature, and the amount of CO2 recovered from the amine solution can be increased.
However, since the known apparatus consumes a great deal of energy so as to generate high-temperature steam of about 120° C., many energy reduction systems have been suggested to date. Examples of these systems include a system in which the temperature of the amine solution in the regeneration tower (regeneration temperature) is decreased to about 100° C.
The known apparatus system has a low-temperature regeneration tower that performs regeneration at a temperature of, for example, 100° C.; and a high-temperature regeneration tower that performs regeneration at a temperature of, for example, 120° C. In this system, the entire amount of energy used for CO2 recovery is less than that used in the system having only a regeneration tower that performs regeneration at a temperature of 120° C. However, the system disclosed requires a 120° C. heat source to be used for the high-temperature regeneration tower.
Further, when an amine solution is heated by high-temperature steam as in the known system, the vapor-containing CO2 separated from the amine solution and the amine solution from which CO2 is separated have a high temperature. Therefore, the system causes a large loss in sensible heat and/or latent heat due to the cooling of the vapor-containing CO2, as well as a large loss in sensible heat by the cooling of the amine solution.